1 files changed, 57 insertions, 0 deletions

diff --git a/tools/perf/util/stat.c b/tools/perf/util/stat.c
new file mode 100644
index 000000000000..23742126f47c
--- /dev/null
+++ b/tools/perf/util/stat.c
@@ -0,0 +1,57 @@
+#include <math.h>
+
+#include "stat.h"
+
+void update_stats(struct stats *stats, u64 val)
+{
+        double delta;
+
+        stats->n++;
+        delta = val - stats->mean;
+        stats->mean += delta / stats->n;
+        stats->M2 += delta*(val - stats->mean);
+}
+
+double avg_stats(struct stats *stats)
+{
+        return stats->mean;
+}
+
+/*
+ * http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance
+ *
+ *       (\Sum n_i^2) - ((\Sum n_i)^2)/n
+ * s^2 = -------------------------------
+ *                  n - 1
+ *
+ * http://en.wikipedia.org/wiki/Stddev
+ *
+ * The std dev of the mean is related to the std dev by:
+ *
+ *             s
+ * s_mean = -------
+ *          sqrt(n)
+ *
+ */
+double stddev_stats(struct stats *stats)
+{
+        double variance, variance_mean;
+
+        if (!stats->n)
+                return 0.0;
+
+        variance = stats->M2 / (stats->n - 1);
+        variance_mean = variance / stats->n;
+
+        return sqrt(variance_mean);
+}
+
+double rel_stddev_stats(double stddev, double avg)
+{
+        double pct = 0.0;
+
+        if (avg)
+                pct = 100.0 * stddev/avg;
+
+        return pct;
+}